Method, base station and mobile station for tdd operation in a communication system

ABSTRACT

A method, NodeB and User Equipment for TDD operation in a communication system operating in TDD mode in a frequency band allocated for FDD operation. Preferably, operation is in TDD uplink and downlink mode in a first frequency band designated or normally used for FDD uplink communication, and in TDD downlink-only mode in a second frequency band designated or normally used for FDD downlink communication. The invention provides the following advantages: Provides a flexible method to deploy a time division duplex architecture in frequency division duplex spectrum. Allows flexible use of system capacity by adjusting the uplink and downlink capacity split. Removes previous FDD duplex restrictions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of and is based upon and claims thebenefit of priority under 35 U.S.C. §120 for U.S. Ser. No. 10/544,451filed Jun. 16, 2006, the entire contents of which are incorporatedherein by reference. U.S. Ser. No. 10/544,451 is a National Stage ofPCT/GB2004/000526, filed Feb. 11, 2004, and claims the benefit ofpriority under 35 U.S.C. §119 from United Kingdom Patent Application No.0303079.8, filed Feb. 11, 2003.

FIELD OF THE INVENTION

This invention relates to communication systems and particularly TimeDivision Duplex (TDD) operation in cellular communication systems.

BACKGROUND OF THE INVENTION

In the field of this invention it is known that first and secondgeneration cellular standards all use “Frequency Division Duplex” (FDD)in which there are separate downlink (base station to mobile) and uplink(mobile to base station) frequency allocations. These allocations areseparated by a “duplex spacing” to prevent interference between thesimultaneous transmission and reception taking place at both the basestation and mobile. FDD allocations are typically termed “pairedspectrum”.

“Time Division Duplex” (TDD) is used in more recent standards, such as“3^(rd) Generation Partnership Project” (3GPP) “Time Division-CodeDivision Multiple Access” (TD-CDMA) and 3GPP “Time Division-SynchronousCode Division Multiple Access” (TD-SCDMA). In TDD systems, transmissionand reception takes place alternately in time on the same frequency. TDDis very well suited for packet data communication where uplink anddownlink capacity can easily be adjusted to meet subscriber trafficprofile.

TDD is not used in FDD bands, because of interference concerns. TDD canoperate in the mobile transmit (uplink) portion of a FDD band withoutdetrimental interference. The allocation of TDD channels immediatelyadjacent to the FDD uplink channels in the “International MobileTelecommunications 2000” (IMT-2000, International TelecommunicationUnion designated ‘3G’ band) provides evidence of the feasibility ofthis. The frequency allocation for IMT-2000 is shown in FIG. 1.

However, operation of TDD in the downlink portion of an FDD band isproblematic, because of adjacent channel interference from existing FDDbase stations to the receivers of co-located or nearby TDD basestations, both of which typically transmit at higher power than thecorresponding user terminals.

Consequently, where a wireless operator has an FDD spectrum allocation,TDD technology can normally only be operated in the FDD uplink part ofthe spectrum, leaving the FDD downlink spectrum unutilized andeffectively ‘wasted’.

A need therefore exists for an arrangement, method and unit for TDDoperation in a communication system wherein the abovementioneddisadvantage (s) may be alleviated.

STATEMENT OF INVENTION

In accordance with a first aspect of the present invention there isprovided a method for TDD operation in a communication system as claimedin claim 1.

In accordance with a second aspect of the present invention there isprovided a base station for TDD operation in a communication system asclaimed in claim 8.

In accordance with a third aspect of the present invention there isprovided a mobile station for TDD operation in a communication system asclaimed in claim 15.

BRIEF DESCRIPTION OF THE DRAWINGS

One method, base station and mobile station for TDD operation in acommunication system incorporating the present invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings, in which:

FIG. 1 shows a block schematic illustration of IMT-2000 frequencyallocation;

FIG. 2 shows a block schematic illustration of TDD with auxiliarydownlink utilization; and

FIG. 3 shows a block schematic illustration of system architecture ofTDD with auxiliary downlink.

DESCRIPTION OF PREFERRED EMBODIMENT(S)

The present invention is based on the realization by the inventors thatit is possible to:

-   -   Enable operation of TDD technology in a band allocated as paired        spectrum for FDD    -   Provide the ability to use the FDD downlink spectrum effectively        to provide capacity and therefore avoid wastage. This is        referred to as an auxiliary TDD downlink channel.    -   Avoid detrimental interference in operation of TDD in the FDD        downlink spectrum.    -   Remove the fixed duplex frequency separation requirement.

An example of TDD operation with auxiliary downlink is shown in FIG. 2.As illustrated, standard TDD operates in the uplink FDD spectrum (210)while the auxiliary downlink operates in the downlink FDD spectrum(220). In the illustration, an example of a 15-time slot frame structureis shown. An upward pointing arrow in a radio frame denotes an uplinktime slot, and a downward pointing arrow denotes a downlink time slot.As can be seen, system capacity is expanded by use of the auxiliarydownlink.

FIG. 3 shows the basic architecture of a 3GPP cellular communicationsystem 300 incorporating the present invention. As illustrated, a NodeB(or base station) 310 is controlled (over the ‘Iub’ interface) by aRadio Network Controller (RNC) 320 and communicates over the Uu radiointerface with User Equipment (UE or mobile terminal) 330.

It will be understood that in other respects the system 300 operates inaccordance with relevant 3GPP Technical Specifications (available at thewebsite http://www.3gpp.org), and need not be described in furtherdetail herein. However, as will be explained further below, for theNodeB 320 the following is to be noted that the base station (NodeB)includes a lower band logical unit 322 and an upper band logical unit324 and operates in both the upper (FDD downlink) and lower (FDD uplink)bands simultaneously, under the control of the RNC 310.

The lower band logical unit 322 supports normal TDD operation, where theradio resource is divided into time slots.

The upper band logical unit 324 supports auxiliary downlink operation.This logical unit supports downlink operation only. The radio resourceis divided into time slots.

In the system of FIG. 3, three types of UE 330 can be supported:

-   -   1. Single frequency standard TDD UE (not shown):        -   This is the standard TDD UE where both uplink and downlink            operate on a single frequency. This type of UE will operate            by communicating with the lower band logical unit in the            NodeB.    -   2. Single instantaneous frequency UE (not shown):    -   This type of UE is able to tune to two different frequencies        (the lower and upper FDD bands) in the same TDD frame under the        control of the network. The UE operates uplink transmission in        the lower FDD band. The UE can operate in either the standard        TDD downlink (lower FDD band) or auxiliary downlink (upper FDD        band) under the control of the network.    -   3. Dual simultaneous frequency UE 330:    -   This type of UE has a lower band UL/DL logical unit 332, an        upper ‘Aux DL’ logical unit 334 and an ‘Aux DL’ Capability        Messaging logical unit 336, and is able to simultaneously tune        to both the lower and upper FDD bands. The UE operates uplink        transmission in the lower FDD band. The UE operates standard TDD        downlink (lower FDD band) and auxiliary downlink (upper FDD        band) under the control of the network. With dual simultaneous        frequency capability the UE is able to operate with increased        downlink capacity.

In operation of the system of FIG. 3, the auxiliary downlink (‘Aux DL’)capability allows an inherently TDD technology to efficiently utilizethe FDD downlink band, avoiding wastage of spectrum, and the downlinkresource in the lower and upper bands is treated as a combined ‘singlepool’ resource, which can be allocated to users according to demand. TheNodeB 320 provides common signalling for both TDD frequencies.

At any time, an individual UE that can support the ‘Aux DL’ mode ofoperation may be allocated downlink capacity in the lower band or upperband or both.

UEs and NodeBs exchange ‘Aux DL’ capability messages, such that theNodeBs and UEs with and without the ‘Aux DL’ feature can co-exist in thenetwork and each operate to the best of their respective abilities.

A UE that does not support auxiliary downlink, e.g., a roaming UE fromanother TDD network, is compatible with the auxiliary downlinkarchitecture by operating in standard TDD mode in lower band. In thiscase, the auxiliary downlink feature is transparent to the UE.

While the Auxiliary Downlink increases the total downlink capacity, italso enables uplink capacity to be increased, as additional timeslotscan be allocated in the lower TDD band to uplink traffic channels.

The separation of the lower and upper band is not restricted by thestandard FDD duplex frequency separation. The UE is instructed by thenetwork to tune to the correct frequency for the auxiliary downlink. Atthe network level the auxiliary downlink in the upper band can even beadjacent to the lower band (even though the UE may be required tooperate only on one downlink frequency at one time to minimize thereceive filtering requirements). This effectively allows the operator todeploy the proposed TDD technology in contiguous frequency allocation.

It will be understood that the arrangement, method and unit for TDDoperation in a communication system described above provides thefollowing advantages:

-   -   Provides a flexible method to deploy a time division duplex        architecture in frequency division duplex spectrum.    -   Allows flexible use of system capacity by adjusting the uplink        and downlink capacity split.    -   Removes previous FDD duplex restrictions.

1. A base station for communicating with a user equipment in a wirelesscommunication system supporting multiple access, wherein the basestation comprises a lower down link frequency carrier unit forcommunicating in a first frequency channel and an upper down linkfrequency carrier unit for communicating in a second frequency channel,and wherein the base station is operable to communicate simultaneouslywith the user equipment in both lower and upper frequency channels in apaired band assigned to a mobile network operator.
 2. A base stationaccording to claim 1, wherein the lower down link frequency carrier unitis arranged to operate in an uplink and downlink mode in the firstfrequency channel and the upper down link frequency carrier unit isarranged to operate in a downlink-only mode in a second frequencychannel allocated.
 3. A base station according to claim 1, wherein thebase station is configured to employ common signalling for the first andsecond frequency channels.
 4. A base station according to claim 1,wherein the base station is configured to exchange messages with a userequipment of the system to establish whether the user equipment iscapable of operating in a first duplex mode in one of the frequencychannels allocated for operation in a second duplex mode.
 5. A basestation according to claim 1, wherein the base station is configured tomanage a plurality of frequencies as a single resource.
 6. A basestation according to claim 1, wherein the lower down link frequencycarrier unit is operable to increase uplink capacity by increasing anallocation of uplink time slots in the first frequency channel.
 7. Abase station according to claim 1, wherein the system comprises a 3GPPsystem and the base station comprises a Node B.
 8. User equipment forcommunicating with a base station in a wireless communication systemsupporting multiple access, wherein the user equipment comprises a lowerdown link frequency carrier unit for communicating in a first frequencychannel and an upper down link frequency carrier unit for communicatingin a second frequency channel, wherein the user equipment is operable tocommunicate simultaneously with a base station in both the lower andupper frequency channels in a paired band assigned to a mobile networkoperator.
 9. User equipment according to claim 8, wherein the lower downlink frequency carrier unit is arranged to operate in an uplink anddownlink mode in a first frequency channel allocated for uplinkcommunication; and the upper down link frequency carrier unit isarranged to operate in a downlink-only mode in a second frequencychannel allocated for downlink communication.
 10. User equipmentaccording to claim 9, wherein user equipment is configured to employcommon signalling for the first and second frequency channels.
 11. Userequipment according to claim 8, wherein the user equipment is configuredto exchange messages with the base station to indicate the userequipment is capable of operating in a first duplex mode in a frequencychannel allocated for operation in a second duplex mode.
 12. Userequipment according to claim 8, wherein the lower down link frequencycarrier unit is operable to increase uplink capacity by increasing theallocation of uplink time slots in the first frequency channel.
 13. Userequipment according to claim 8, wherein the wireless communicationsystem comprises a 3GPP wireless communication system.
 14. Userequipment for use in a wireless communication system supporting multipleaccess, wherein the user equipment is configured to operate in upper andlower down link carrier frequencies in a paired band assigned to amobile network operator, and to treat the upper and lower down linkcarrier frequencies as a single combined resource for downlinkallocation,
 15. User equipment according to claim 14, wherein the userequipment comprises a lower down link frequency carrier unit and anupper down link frequency carrier unit, the lower down link frequencycarrier unit arranged to operate using an uplink and downlink carrier ina first frequency channel allocated for uplink communication; and theupper down link frequency carrier unit is arranged to operate using adownlink-only carrier in a second frequency channel allocated fordownlink communication.
 16. User equipment according to claim 15,wherein the user equipment is configured to employ common signalling forthe first and second frequency channels.
 17. User equipment according toany one of claim 14, wherein the user equipment is operable to exchangemessages with a base station to indicate the user equipment is capableof operating in a first duplex mode in a frequency channel allocated foroperation in a second duplex mode.
 18. User equipment according to claim15, wherein the lower down link frequency carrier unit is operable toincrease uplink capacity by increasing the allocation of uplink timeslots in the first frequency channel.
 19. User equipment according toclaim 14, wherein the wireless communication system comprises a 3GPPwireless communication system.
 20. A base station for use in a wirelesscommunication system supporting multiple access, wherein the basestation is configured to operate in upper and lower down link carrierfrequencies in a paired band assigned to a mobile network operator, andto treat the upper and lower down link carrier frequencies as a singlecombined resource for downlink allocation.
 21. A base station accordingto claim 20, wherein the base station comprises a lower down linkfrequency carrier unit and an upper down link frequency carrier unit,the lower down link frequency carrier unit arranged to operate using anuplink and downlink carrier in a first frequency channel allocated foruplink communication; and the upper down link frequency carrier unit isarranged to operate using a downlink-only carrier in a second frequencychannel allocated for downlink communication.
 22. A base stationaccording to claim 21, wherein the base station is configured to employcommon signalling for the first and second frequency channels.
 23. Abase station according to and one of claims 20, wherein the base stationis operable to exchange messages with a user equipment to establishwhether the user equipment is capable of operating in a first duplexmode in a frequency channel allocated for operation in a second duplexmode and accordingly communicating with the base station.
 24. A basestation according to claim 21, wherein the lower down link frequencycarrier is operable to increase uplink capacity by increasing theallocation of uplink time slots in the fast frequency channel.
 25. Abase station according to claim 20, wherein the wireless communicationsystem comprises a 3GPP system and the base station comprises a Node B.26. A method of communicating by a base station in a wirelesscommunication system supporting multiple access, the method comprising,communicating from the base station using upper and lower down linkcarrier frequencies in a paired band assigned to a mobile networkoperator, and treating the upper and lower down link carrier frequenciesas a single combined resource for downlink allocation.
 27. A methodaccording to claim 26, further comprising: operating in an uplink anddownlink mode in a first frequency channel allocated for uplinkcommunication; and operating in a downlink-only mode in a secondfrequency channel allocated for downlink communication.
 28. A methodaccording to claim 27, further comprising employing common signallingfor the first and second frequency channels.
 29. A method according toclaim 26, comprising exchanging messaging between a base station and theuser equipment to establish whether the user equipment is capable ofoperating in a first duplex mode in a frequency channel allocated foroperation in a second duplex mode and accordingly communicating betweenthe base station and the user equipment.
 30. A method according to claim26, further comprising managing a plurality of frequencies as a singleresource.
 31. A method according to claim 27, comprising increasinguplink capacity by increasing an allocation of uplink time slots in thefirst frequency channel.
 32. A method of communicating by a userequipment in a wireless communication system supporting multiple access,the method comprising, communicating with a base station using upper andlower down link carrier frequencies in a paired band assigned to amobile network operator, wherein the upper and lower down link carrierfrequencies are treated as a single combined resource for allocation.33. A wireless communication system supporting multiple accesscomprising a base station and a user equipment, wherein the base stationand user equipment are configured to communicate with one another usingupper and lower down link carrier frequencies in a paired band assignedto a mobile network operator, wherein the upper and lower down linkcarrier frequencies are treated as a single combined resource forallocation.
 34. A method of communicating in a wireless communicationsystem supporting multiple access, the method comprising communicatingbetween a base station and a user equipment using upper and lower downlink carrier frequencies in a paired band assigned to a mobile networkoperator, wherein the upper and lower down link carrier frequencies aretreated as a single combined resource for allocation.